This application relates to multi-circuit heat pump systems that are capable of operating in both cooling and heating modes. Further, these systems are provided with the circuits that have the ability to independently operate in various regimes in order to satisfy a wide spectrum of sensible and latent capacity demands. Typically, these systems have a reheat coil(s), incorporated into the system design to provide a reheat function, and additional control means capable of alternating between operational regimes independently for each circuit in response to environmental conditions and load demands.
Refrigerant systems are utilized to control the temperature and humidity of air in various environments to be conditioned. One type of a refrigerant system is a heat pump that can operate in a cooling mode or heating mode. Typically, in a cooling mode, a refrigerant is compressed in a compressor and delivered to an outdoor heat exchanger. In the outdoor heat exchanger, heat is exchanged between outside ambient air and the refrigerant. From the outdoor heat exchanger, the refrigerant passes to an expansion device in which the refrigerant is expanded to a lower pressure and temperature, and then to an indoor heat exchanger. In the indoor heat exchanger, heat is exchanged between the refrigerant and the indoor air, to condition the indoor air. When the cooling mode is in operation, an indoor heat exchanger cools the air that is being supplied to the indoor environment. In addition, as the temperature of the indoor air is lowered, moisture usually is also taken out of the air. In this manner, the humidity level of the indoor air can also be controlled.
In the heating mode, the refrigerant flow through the system is essentially reversed. The indoor heat exchanger becomes the condenser and releases heat into the environment to be conditioned (heated in this case) and the outdoor heat exchanger becomes the evaporator and exchanges heat with a relatively cold outdoor air. Heat pumps are known as the systems that can reverse the refrigerant flow through the refrigerant cycle in order to operate in both heating and cooling modes. This is usually achieved by incorporating a four-way valve or an equivalent device into the system schematic downstream of the compressor discharge port. The four-way valve selectively directs the discharge refrigerant flow through the indoor or outdoor heat exchanger when the system is in the heating or cooling mode of operation respectively. Furthermore, if the expansion device is not capable of handling the reversing flow, then, for example, a pair of unidirectional expansion devices, each along with the corresponding check valve, is to be employed instead.
In some cases, the temperature level, to which the air is brought to provide comfort environment in the conditioned space, may need to be higher than the temperature that would provide the ideal humidity level. Such corresponding levels of temperature and humidity may vary from one application to another and are highly dependent on environmental and operating conditions. This has presented design challenges to refrigerant cycle designers. One way to address such challenges is to utilize reheat coils. In many cases, the reheat coils, placed in the path of the indoor air stream behind the indoor heat exchanger, are employed for the purpose of reheating the air supplied to the conditioned space after it has been overcooled in the indoor heat exchanger for moisture removal.
Multi-circuit refrigerant systems are also applied in the industry, wherein several independent circuits operate under a single control to provide various levels of sensible and latent capacity in response to the external load demands and wherein each circuit can independently function in one of several operational regimes.
A further option available to a refrigerant system designer is to integrate a reheat coil(s) in the schematics for at least one of the refrigerant circuits of a multi-circuit system. As mentioned above, in a reheat coil, at least a portion of the refrigerant upstream of the expansion device is passed through a reheat heat exchanger and then is returned back to the main circuit, and at least a portion of the conditioned air having passed over the indoor heat exchanger is then passed over this reheat heat exchanger to be reheated to a desired temperature.
However, multi-circuit heat pump systems have not been provided with the reheat function.